When connected to the outlet it will be running solely on outlet power just by default, you don't need to do anything specific.
Edit: Now that I re-read this OP, it sounds more like you want to stop the battery from charging when connected to AC.
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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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When connected to the outlet it will be running solely on outlet power just by default, you don't need to do anything specific.
Edit: Now that I re-read this OP, it sounds more like you want to stop the battery from charging when connected to AC.